Multi-Subtarget Metrology Target for Lithographic Process Control
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Solution Overview
Problem
Current metrology techniques in lithographic processes face challenges in improving throughput, flexibility, and accuracy, especially when measuring small target structures, and are limited in their ability to handle significant variations in the process stack and multi-layer overlay measurements.
Innovation Solution
A diffraction measurement target with multiple sub-targets, each having a different periodic structure design, is used to measure various lithographic process parameters simultaneously, allowing for improved accuracy and flexibility by detecting radiation scattered from these sub-targets to obtain measurements representing different process parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple separate metrology targets are used to measure different lithographic parameters, then measurement accuracy for each parameter can be optimized, but measurement throughput decreases due to multiple measurement sequences
Solution Approach 1:
The patent combines multiple separate metrology targets into a single integrated target structure. Each sub-target (first sub-target for overlay measurement, second sub-target for critical dimension measurement, third sub-target for focus measurement) is merged into one target that can be measured simultaneously in a single measurement sequence, thereby improving throughput while maintaining the specialized measurement capabilities for each parameter type
Solution Approach 2:
The integrated metrology target serves multiple functions within a single structure. It enables overlay measurement, critical dimension measurement, and focus measurement all through one target, making the measurement system universal and eliminating the need for separate measurement sequences for different parameters
2Productivity
If a single metrology target design is used for all measurements, then measurement throughput increases with a single measurement sequence, but measurement precision for specific parameters decreases due to design compromises
Solution Approach 1:
Different regions of the integrated target (different sub-targets) have specialized designs optimized for specific measurement types. The first sub-target has a design optimized for overlay measurement, the second for critical dimension, and the third for focus measurement. This local specialization ensures high precision for each parameter while maintaining overall throughput efficiency
3Ease of manufacture
If the metrology target design is simplified for ease of manufacture, then manufacturing complexity decreases, but the ability to handle process stack variations and multi-layer overlay measurements is reduced
Solution Approach 1:
The target is segmented into multiple distinct sub-targets, each with specialized designs for handling different measurement challenges. This segmentation allows each sub-target to be optimized for specific process conditions and layer configurations, enhancing versatility in handling process variations while maintaining a modular structure that is relatively easy to manufacture
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the measurement capabilities, enabling more efficient process control and increased throughput by allowing multiple parameters to be measured in a single measurement sequence, effectively handling process stack variations and multi-layer overlay measurements within a compact target design.
Implementation Method 1
detecting radiation scattered by the at least two sub-targets to obtain for that target a measurement representing the different parameters of the lithographic process
Data Source
AI summary
A method of measuring a parameter of a lithographic process, the method including: illuminating a diffraction measurement target on a substrate with radiation, the measurement target including at least a first sub-target, at least a second sub-target and at least third sub-target, wherein the first, second and third sub-targets each include a periodic structure and wherein the first sub-target, second sub-target and third sub-target each have a different design and wherein at least two of the sub-targets are respectively designed for determination of a different lithographic process parameter; and detecting radiation scattered by the at least two sub-targets to obtain for that target a measurement representing the different parameters of the lithographic process.